The detoxification of hazardous waste such as certain organic compounds, medical waste contaminated with pathogens, and low level radioactive waste, is an ongoing problem for many industries. The shipment of such waste to disposal sites creates significant danger of environmental release in the event of an accident, and the volume available as landfill sites is rapidly disappearing while costs are increasing rapidly. Accordingly, there is a need for methods and systems to efficiently dispose or reduce the volume of such toxic waste at the site where the waste is generated.
The use of incinerators for burning hazardous waste is becoming unacceptable. Incinerators that meet current air pollution laws and have efficient operation tend to be relatively large and therefore may not be economically feasible for placement at facilities where toxic waste is generated. Moreover, incinerators are often difficult to control and create strong community and political ill-feeling. Perhaps more importantly, however, the incineration process may produce other toxic products which are themselves undesirable and which are difficult or impossible to eliminate.
In U.S. Pat. No. 4,874,587, issued Aug. 26, 1987 and assigned to the assignee of the present invention, a process and apparatus are described for hazardous waste detoxification which represent a significant improvement over incinerators. In the aforesaid patent, a reactor is described in which toxic destruction levels of 99.99% or more are achieved. The aforesaid process and apparatus are operated without air or free oxygen reaction and produce an effluent gas which is primarily comprised of carbon dioxide, hydrogen, and water. The process and apparatus described in the aforesaid patent has been classified by the United States Environmental Protection Agency as "thermolytic detoxification" as differentiated from "incineration".
A thermolytic detoxification reactor operates to react a gaseous stream of toxic material with water in excess of the stoichiometric amount necessary to react with substantially all of the organic compounds in the stream of toxic waste. This reaction is carried out at a temperature in excess of about 250.degree. C. and results in an effluent gas stream of high temperature comprised primarily of carbon dioxide, water, and hydrogen but also containing low levels of carbon monoxide. The latter can be readily converted to carbon dioxide by catalytic oxidation.
Since the principal reaction in a thermolytic detoxification reactor occurs in the gas phase, the processing of liquid and semi-solid waste, where the waste material can be relatively easily gasified, is fairly straightforward. For example, a system for vaporizing and gasifying toxic waste for feeding to a thermolytic detoxification reactor wherein the toxic waste is liquid contained in a metal drum is shown and described in U.S. Pat. No. 4,863,702, issued on Sep. 5, 1989 and assigned to the assignee of the present invention. In the case of solid waste, however, conversion of the waste into a gaseous form for feeding to a thermolytic detoxification reactor is not as straightforward as in the case of liquids and semi-solids. Melting, incineration or direct gassification of such solid materials prior to feeding into the thermolytic detoxification reactor may be possible for some materials. However, for many materials proper preparation would necessitate a totally separate additional system based on a different technology, substantially increasing capital expense and energy cost.
Accordingly, it is an object of this invention to provide an improved method and system for detoxifying solid toxic waste.
Another object of the invention is to provide an improved method for detoxifying solid toxic waste which employs a thermolytic detoxification reactor and which is adaptable to on-site applications.
Still another object of the invention is to provide an improved method and apparatus for detoxifying solid toxic waste which minimizes environmental hazards in the feeding of the waste, the processing of the waste, and the disposal of residues.
Other objects of the invention will become apparent to those skilled in the art from the following description and accompanying drawings.